| ( | 18 | − | x | ) | ( | 300 | + | 3 | x | ) | = | 5850 |
| Left side of the equation = | 18 | ( | 300 | + | 3 | x | ) | − | x | ( | 300 | + | 3 | x | ) |
| = | 18 | × | 300 | + | 18 | × | 3 | x | − | x | ( | 300 | + | 3 | x | ) |
| = | 5400 | + | 54 | x | − | x | ( | 300 | + | 3 | x | ) |
| = | 5400 | + | 54 | x | − | x | × | 300 | − | x | × | 3 | x |
| = | 5400 | − | 246 | x | − | x | × | 3 | x |
| 5400 | − | 246 | x | − | x | × | 3 | x | = | 5850 |